Check that floats are in the IEEE 754 format when building with CMake

SCons version is coming a bit later.

CMakeLists.txt

@@ -55,6 +55,15 @@ option(ENABLE_OMP "Enables OpenMP, and has additional dependencies" OFF)
 option(ENABLE_LIBPNG "Enable support for writing png files (screenshots, images)" ON)
 option(ENABLE_HISTORY "Enable using GNU history for history in lua console" ON)
 
+if(NOT CMAKE_CROSSCOMPILING)
+	try_run(IEEE754_TEST_RETURN_CODE IEEE754_TEST_COMPILED ${CMAKE_BINARY_DIR} ${CMAKE_SOURCE_DIR}/src/compile_time_tests/ieee_754.cpp)
+	if(NOT IEEE754_TEST_RETURN_CODE EQUAL 0)
+		message(FATAL_ERROR "Your platform does not represent floating point numbers in the IEEE 754 format.")
+	endif()
+else()
+	message(WARNING "You are cross-compiling. Skipping IEEE 754 test.")
+endif()
+
 if(DEFINED ENV{TRAVIS})
 	find_package(SDL2 2.0.2 REQUIRED)
 else()

src/compile_time_tests/ieee_754.cpp

@@ -0,0 +1,17 @@
+#include <cstdint>
+
+// This test verifies that floating point numbers are represented in the IEEE 754 format.
+// Wesnoth requires that.
+int main()
+{
+	union
+	{
+		double floating_point_number;
+		uint64_t integer;
+	} number;
+
+	number.floating_point_number = 1.2;
+	// Return code zero means success.
+	// Thus, check that the bit representation is *not* what IEEE 754 specifies.
+	return number.integer != 0x3FF3333333333333ull;
+}